Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk drive 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a spindle S1 of motor 14, an actuator 18 and an arm 20 attached to a spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a magnetoresistive read element (shown in FIG. 1C). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to “fly” above the magnetic disk 16. Various magnetic “tracks” of information can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk drives is well known to those skilled in the art.
FIG. 1C depicts a magnetic read/write head 30 including a write element 32 and read element 34. The edges of the write element 32 and read element 34 also define an air bearing surface ABS in a plane 33, which flies above the surface of the magnetic disk 16 during operation.
Read element 34 includes a first shield 44, an intermediate layer 38 which serves as a second shield, and a read sensor 46 located between the first shield 44 and the intermediate layer 38. The read sensor 46 has a particular stripe height, SH, and a particular location between the first shield 44 and the second shield 38, both of which are chosen to attain particular read performance. Control of stripe height is important in controlling device resistance, device output amplitude, device bias point and consequently many related measures of performance. MR sensors can be used with a variety of stripe heights, with a typical SH being smaller than about 2 microns, including much less than 1 micron. Further, although the read sensor 46 is shown in FIG. 1C as a shielded single-element vertical read sensor, the read element 34 can take a variety of forms as is known to those skilled in the art, such as unshielded read sensors. The design and manufacture of magnetoresistive heads, such as read sensor 46, are well known to those skilled in the art.
Write element 32 is typically an inductive write element including the intermediate layer 38 which serves as a first yoke element or pole, and a second yoke element or pole 36, defining a write gap 40 therebetween. The first yoke element 38 and second yoke element 36 are configured and arranged relative to each other such that the write gap 40 has a particular nose length, NL. Also included in write element 32, is a conductive coil 42 that is positioned within a dielectric medium 43. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16.
The formation of a read/write head 30 begins with a wafer 50, as shown in FIG. 1D, which includes, formed over a substrate, sets of several layers or films of various materials that form an array of read/write heads (not shown), including the elements of the read/write head 30 that are shown in FIG. 1C. The wafer 50 is then divided into multiple slider bars 52 such that each slider bar 52 has a first cut surface, or edge, 54 and a second cut surface, or edge, 56 substantially parallel to each other. As can be better seen in FIG. 1E, each slider bar 52 may include several read/write heads 60 in series along the bar. For example, a typical slider bar may include about fifty to sixty (50-60) read/write heads 60. As is shown in FIG. 1E, the read/write heads 60 can be of different configuration, however, alternatively each of the write/read heads 60 along the slider bar 52 can be of approximately the same configuration.
As is shown in FIG. 1E, the second cut surface 56 is formed such that the read/write heads 60 extend through to the second cut surface 56. Thus, at the second cut surface 56, the read/write heads 60 are exposed and therefore available for removing material along the second cut surface 56 in a process termed lapping. Alternatively, the read/write heads 60 can extend to near the second cut surface 56, without being initially exposed. In such a case, the read/write heads 60 can become exposed and material can be removed therefrom during the lapping process.
The goal of lapping is to remove material from the second cut surface 56, which defines a lapping plane L, to form the ABS (also shown in FIG. 1C) of each of the read/write heads 60 in the plane 33. More particularly, it is the objective of the lapping process to define the ABS at a precise predetermined distance from the upper edge 64 of the read sensor 46 where the upper edge 64 is defined by wafer processes. In this way, the stripe height SH of the read sensor 46 (shown in FIG. 1C) is defined substantially orthogonal to the lapping plane L, and the nose length NL is similarly defined substantially orthogonal to the lapping plane L. After lapping, the read/write heads are then each cut from the slider bar to form individual read/write heads.
FIG. 1F shows a typical lapping machine 70. The slider bar 52 is held along the first cut surface 54 by a jig 72. In turn, the jig 72 is contacted by pistons 74 at various bending points 76 along the length of the jig 72. Pistons 74 may be, for example, dual action air cylinders, and are configured to deflect the jig 72 at the bending points 76 by a particular amount. To obtain this particular amount, a controller 78 is used to regulate the operation of the pistons 74. The slider bar 52 is further oriented such that the second cut surface 56 lies substantially parallel to an upper surface 80 of a lapping plate 82. During lapping, an abrasive material, for example a diamond slurry, is introduced between the second cut surface 56 of the slider bar 52 and the upper surface 80 of the lapping plate 82. When the second cut surface 56 is brought into contact or near-contact with the upper surface 80, the slider bar 52 and the lapping plate 82 are moved relative to each other within the plane defined by the second cut surface 56 and the upper surface 80. This movement, along with the forces acting to press together the upper surface 80 and the second cut surface 56 and with the abrasive material placed therebetween, acts to abrasively lap the second cut surface 56 and thereby the read/write heads 60.
Because of the critical nature of the stripe height, SH, it is important to end the lapping process at the particular point which attains the correct stripe height. While lapping times, lapping pressures, and other lapping parameters could be standardized for particular types of slider bars 52, such a method can be ineffective due to fabrication variations such as in the deposition of materials of the read/write heads 60, or the wafer cut locations relative to the read/write heads. More particularly, some fabrication variations may exist within a single slider bar or a single wafer, with variations increasing with distance, while others may exist between different wafers (i.e., wafer-to-wafer variation). Additionally, as the read and write elements of a single read/write head are separated from one another by some distance, it is important for the lapping process to proceed at the correct angle, such that both the SH and the NL of the lapped read/write head are properly oriented with respect to the second cut surface. Therefore, it is beneficial for the controller to have some indication or feedback of the actual stripe height of the read sensor 46 during the lapping process.